If repetition is for the sake of emphasis, then the Bible is loud and clear about the necessity of holiness. In his book, The Hole In Our Holiness, Kevin DeYoung writes,
There’s no question holiness is one of the central themes in the Bible. The word “holy” occurs more than 600 times in the Bible, more than 700 when you include derivative words like holiness, sanctify, and sanctification. You can’t make sense of the Bible without understanding that God is holy and that this holy God is intent on making a holy people to live with him forever in a holy heaven. (p.31)
So if we are neglecting holiness and the lifelong pursuit of sanctification in Christ, it is not for lack of instruction or emphasis in Scripture.
Holiness is not an optional extra or add-on to the Christian life. If anything, it is the distinguishing characteristic of every believer. Quoting Leviticus 11:44, the Apostle Peter writes,
As obedient children, do not be conformed to the passions of your former ignorance, but as he who called you is holy, you also be holy in all your conduct, since it is written, “You shall be holy, for I am holy.” (1 Peter 1:14-16 ESV)
An unholy Christian is a contradiction in terms.